Method for fabricating liquid crystal display panel

ABSTRACT

A method for fabricating a liquid crystal display panel includes forming a main UV sealant to surround a plurality of unit cells on either one of first and second substrates, the dummy UV sealant formed at an outside of the main UV sealant, dropping at least one droplet of liquid crystal onto either one of the first and second substrates, attaching the first and second substrates, irradiating a UV ray on the attached substrates with masking regions where the dummy UV sealant and at least one scribing line are crossed, thereby bonding the substrates, and cutting the bonded substrates into a plurality of unit cells.

This application claims the benefit of the Korean Application No.P2002-12056 filed on Mar. 7, 2002, which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display, and moreparticularly, to a method for fabricating a liquid crystal display (LCD)panel by a liquid crystal dropping method.

2. Discussion of the Related Art

A thin flat panel display tends to have a thickness of no more than afew centimeters. Particularly, a liquid crystal display (LCD) has a widescope of applications, such as notebook computers, computer monitors,gauge monitors for space crafts, and air crafts, and the like.

In general, the LCD is provided with a lower substrate having thin filmtransistors and pixel electrodes formed thereon, an upper substrateopposite to the lower substrate having a black matrix (BM), a colorfilter layer, and a common electrode, which are formed thereon, and aliquid crystal layer between the two substrates, for driving the liquidcrystal by the electric field generated by the power supply applied tothe pixel electrode and the common electrode between the substrates, toregulate the transmittivity of the liquid crystal, thereby displaying apicture on the display screen.

In the foregoing LCD, a vacuum injection method has been used forforming the liquid crystal layer between the lower substrate and theupper substrate. In such a method, after the lower substrate and theupper substrate are bonded together, a liquid crystal is injectedbetween the two substrates by using capillary phenomenon and a pressuredifference. However, the vacuum injection method takes much time toinject the liquid crystal between the substrates. As a result,productivity is much reduced as the substrate becomes large.

Consequently, a method called a liquid crystal dropping method issuggested for solving such a problem. A method for fabricating an LCDpanel by using a related art liquid crystal dropping method will beexplained with reference to the attached drawings.

FIGS. 1A to 1E illustrate expanded perspective views showing a methodfor fabricating an LCD panel by using a related art liquid crystaldropping method. For convenience, only four unit cells are illustratedin the drawings.

Referring to FIG. 1A, a lower substrate 1 and an upper substrate 3 areprepared for the process. A plurality of gate lines and data lines (bothnot shown) are formed on the lower substrate 1 to cross each otherdefining pixel regions. A thin film transistor is formed at everycrossing point of the gate lines and the data lines. A pixel electrodeis formed at every pixel region connected to the thin film transistor.

A black matrix is formed on the upper substrate 3 for shielding a lightleakage from the gate lines, the data lines, and the thin filmtransistor regions. A color filter layer of red, green, and blue isformed thereon. A common electrode is formed thereon in this order. Anorientation film is formed on both of the lower substrate 1 and theupper substrate 3 for an initial orientation of the liquid crystal.

In FIG. 1B, a main sealant 7 and a dummy sealant 8 are coated on thelower substrate 1, and a plurality of liquid crystal droplets 5 arepositioned thereon to form a liquid crystal layer. Then, spacers (notshown) are spread on the upper substrate 3 for maintaining a cell gap.

The main sealant 7 prevents the liquid crystal from leaking, and bondsthe upper and lower substrates. The dummy sealant 8 is formed at thedummy region on the outside of the main sealant 7. The dummy sealant isto protect the main sealant 7.

In the liquid crystal dropping method, the liquid crystal layer isplaced between the attached substrates before hardening a sealant.Accordingly, if a thermo-hardening sealant is used to bond thesubstrates, it may flow and contaminate the liquid crystal during theheating process. Thus, a UV sealant has to be used as a sealant to avoidsuch a problem.

Referring to FIG. 1C, the lower substrate 1 and the upper substrate 3are attached to each other. As shown in FIG. 1D, a UV ray is irradiatedby using a UV irradiating device 9, to harden the sealant 7 (shown inFIG. 1B), thereby bonding the lower substrate 1 and the upper substrate3. FIG. 1E illustrates the bonded substrates 1 and 3 are cut into aplurality of unit cells.

FIG. 2 illustrates a process for cutting the substrates into the unitcells. In FIG. 2, a scribing line is formed on the surface of the bondedsubstrates 1 and 3 using a scriber, such as a diamond pen having ahardness greater than glass, which is a material of the substrates(scribing process). Thereafter, a mechanical impact is given along thescribing line 10 (break process), to cut into a plurality of unit cells.Alternatively, a diamond pen or wheel may be used, to carry out thescribing process and the breaking process in one process, to obtain theunit cell one by one.

FIG. 2 is provided for illustrating the cell cutting process, and thescribing line is not shown in detail. More scribing lines may be formedto remove the dummy region at the outside of the cell in the actual cellcutting process.

FIG. 3 illustrates a plane view of the scribing lines in detail.Particularly, sealants 7 and 8 formed on the lower substrate 1 areillustrated with the scribing lines 10.

Referring to FIG. 3, the scribing line 10 overlaps a portion of thedummy sealant 8 at the region (shown as circles) when the dummy sealant8 is hardened by the V irradiating process before the cell cuttingprocess.

Consequently, unit cells the hardened dummy sealant 8 does not cause aproblem when the scribing and breaking are processed one by one toobtain unit cells. However, when unit cell one by one by the scribingand breaking are processed at the same time, it will be difficult to cutinto the unit cell due to the hardened dummy sealant 8.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method forfabricating a liquid crystal display panel that substantially obviatesone or more of problems due to limitations and disadvantages of therelated art.

Another object of the present invention is to provide a method forfabricating a liquid crystal display panel, which facilitates an easycell cutting in the simultaneous scribing and breaking processes.

Additional features and advantages of the invention will be set forth inthe description which follows and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a methodfor fabricating a liquid crystal display panel includes forming a mainUV sealant to surround a plurality of unit cells on either one of firstand second substrates, the dummy UV sealant being formed at an outsideof the main UV sealant, dropping at least one droplet of liquid crystalonto either one of the first and second substrates, attaching the firstand second substrates, irradiating a UV ray on the attached substrateswith masking regions where the dummy UV sealant and at least onescribing line are crossed, thereby bonding the substrates, and cuttingthe bonded substrates into a plurality of unit cells.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principle of theinvention.

In the drawings:

FIGS. 1A to 1E are expanded perspective views illustrating a method forfabricating an LCD panel using a related art liquid crystal droppingmethod;

FIG. 2 illustrates a perspective view showing a related art cell cuttingprocess;

FIG. 3 illustrates a plane view showing a plurality of scribing linesand a sealant formed on the lower substrate of a related art LCD;

FIGS. 4A to 4E are expanded perspective views illustrating a method forfabricating an LCD panel according to a first embodiment of the presentinvention; and

FIGS. 5A to 5C are perspective views to illustrate the process of UVirradiation in a method for fabricating an LCD according to a secondembodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to the illustrated embodiments ofthe present invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

FIGS. 4A to 4E are expanded perspective views illustrating a method forfabricating an LCD panel according to a first embodiment of the presentinvention. Although the drawings illustrate only four unit cells, thenumber of the unit cells may be varied depending upon the size of thesubstrate.

Referring to FIG. 4A, a lower substrate 200 and an upper substrate 300are prepared for the process. A plurality of gate lines and data lines(both not shown) are formed on the lower substrate 200 to cross eachother defining pixel regions, a thin film transistor having a gateelectrode, a gate insulating film, a semiconductor layer, an ohmiccontact layer, source/drain electrodes, and protection film, is formedat every crossing point of the gate lines and the data lines. A pixelelectrode is further formed at each of the pixel regions connected tothe thin film transistor.

An orientation film is formed on the pixel electrodes for an initialorientation of the liquid crystal. The orientation film may be formed ofpolyimide, polyamide group compound, polyvinylalcohol (PVA), polyamicacid by rubbing, or a photosensitive material, such aspolyvinvylcinnamate (PVCN) and polysilioxanecinnamate (PSCN).Alternatively, cellulosecinnamate (CelCN) group compound may be selectedby using photo-alignment method.

A light shielding film is formed on the upper substrate 300 forshielding a light leakage from the gate lines, the data lines, and thethin film transistor regions. A color filter layer of red, green, andblue is formed thereon. A common electrode is formed thereon in thisorder. Additionally, an overcoat layer may be formed between the colorfilter layer and the common electrode. The orientation film is formed onthe common electrode.

Silver (Ag) dots are formed at the outside of the lower substrate 200,for applying a voltage to the common electrode on the upper substrate300 after the lower and upper substrates 200 and 300 are bonded witheach other. Alternatively, the silver dots may be formed on the uppersubstrate 300.

In an in plane switching (IPS) mode LCD, a lateral field is induced bythe common electrode formed on the lower substrate the same as the pixelelectrode. The silver dots are not formed on the substrates.

Referring to FIG. 4B, a main UV sealant 700 is coated on the uppersubstrate 300 in a closed pattern, and a dummy UV sealant 800 is formedat the outside of the main UV sealant 700 in a closed pattern. Thesealant may be coated by using a dispensing method or a screen printingmethod. However, the screen printing method may damage the orientationfilm formed on the substrate since the screen comes into contact withthe substrate. Also, the screen printing method may not be economicallyfeasible due to a large amount of the sealant loss in a large substrate.

Then, the liquid crystal droplets 500 are placed onto the lowersubstrate 200 to form a liquid crystal layer. The liquid crystal may becontaminated when the liquid crystal meets the main sealant 700 beforethe main sealant 700 is hardened. Therefore, the liquid crystal dropletsmay have to be dropped onto the central part of the lower substrate 200.The liquid crystal droplets 500 dropped at the central part spreadslowly even after the main sealant 700 is hardened, so that it isdistributed evenly throughout the entire substrate with the sameconcentration.

FIG. 4B illustrates that both the liquid crystal droplets 500 and thesealants 700 and 800 are coated on the lower substrate 200. However, asan alternative in practicing the present invention, the liquid crystaldroplets 500 may be formed on the upper substrate 300, while the UVsealants 700 and 800 may be coated on the lower substrate 200.

Moreover, the liquid crystal droplets 500 and the UV sealants 700 and800 may be formed on the same substrate. However, the liquid crystal andthe sealant may have to be formed on different substrates in order toshorten the fabrication time period. When the liquid crystal droplets500 and the UV sealants 700 and 800 are formed on the same substrate,there occurs an unbalance in the fabricating process between thesubstrate with the liquid crystal and the sealant and the substratewithout the liquid crystal. For example, the substrate may not becleaned when the sealant is contaminated before the substrates areattached to each other since the liquid crystal and the sealant areformed on the same substrate.

Spacers may be formed on either of the two substrates 200 or 300 formaintaining a cell gap. The spacers may be sprayed at a high pressureonto the substrate from a spray nozzle mixed with ball spacers and asolution having an appropriate concentration. Alternatively, columnspacers may be formed on portions of the substrate of the gate lines ordata lines: The column spacers may be used for the large sized substratesince the ball spacers may cause an uneven cell gap for the large sizedsubstrate. The column spacers may be formed of a photosensitive organicresin.

Referring to FIG. 4C, the lower substrate 200 and the upper substrate300 are attached to each other. The lower substrate 200 and the uppersubstrate 300 may be bonded by the following processes. First, one ofthe substrates having the liquid crystal dropped thereon is placed atthe lower side. The other substrate is turned by 180 degrees so that theside of the substrate at the upper side having layers faces into theupper surface of the substrate at the lower side. Thereafter, thesubstrate at the upper side is pressed, or the space between thesubstrates is evacuated, and releasing the vacuum, thereby attaching thetwo substrates.

Then, referring to FIG. 4D, a mask 950 is placed between the attachedsubstrates 200 and 300 and a UV irradiating device 900 for masking theoverlapping region between the dummy UV sealant 800 and the scribingline. A UV ray is then irradiated thereon. Upon irradiating the UV ray,monomers or oligomers are polymerized and hardened, thereby bonding thelower substrate 200 and the upper substrate 300.

The region masked by the mask 950 is shaded from the UV ray, so that thedummy UV sealant at this region is not hardened. Thus, the dummy UVsealant remains an initial coating condition, i.e., fluidic condition,so that the cell cutting process after the bonding process becomes easy.

Monomers or oligomers each having one end coupled to the acrylic groupand the other end coupled to the epoxy group mixed with an initiator areused as the UV sealants 700 and 800. Since the epoxy group is notreactive with the UV irradiation, the sealant may have to be heated atabout 120° C. for one hour after the UV irradiation for hardening thesealant. However, even if the dummy sealant is eventually hardened bythe thermal process, the hardening ratio drops below 50%, such that thedummy sealant gives no influence to the cell cutting process.

FIG. 4E illustrates that the bonded substrates are cut into theindividual cells. In the cutting process, a cutting device of diamondsuch as a pen or a toothed wheel is used to cut the unit cells one byone along the scribing lines 600 by the simultaneous scribing andbreaking processes. The use of the cutting device that can carry out thesimultaneous scribing and breaking processes may reduce both the spaceoccupied by the device and the cutting time period.

A final inspection (not shown) is carried out after the cutting process.In the final inspection, presence of defects is determined before thesubstrates cut into the unit cells are assembled, by examining anoperation condition of the pixels when a voltage applied thereto isturned on/off.

FIGS. 5A to 5C illustrate expanded perspective views each showing the UVirradiation process in the fabricating method of an LCD in accordancewith a second embodiment of the present invention. All the fabricatingprocess is similar to the first embodiment except for the UV irradiationprocess.

In the simultaneous scribing and breaking processes, when the substratesare cut in up and down directions starting from the scribe line at theend of the right or left side, the dummy UV sealant on the right or leftside may be removed. Therefore, the removed dummy UV sealant gives noinfluence to the following cell cutting process.

Accordingly, the same result may be obtained in with masking the cellcutting process even if the UV ray is irradiated after upper and lowerside regions of the dummy UV sealant overlapped the scribing lines, oronly left and right side regions of the dummy UV sealant overlapped thescribing lines.

FIG. 5A illustrates the UV irradiation process, with masking only upperand lower side regions of the dummy UV sealant overlapping the scribinglines by using a mask 950 a. FIG. 5B illustrates the UV irradiationprocess, with masking only left and right side regions of the dummy UVsealant overlapping the scribing lines by using the mask 950 a. FIG. 5Ais applicable to an embodiment where upper and lower end portions arecut first, while FIG. 5B is applicable to an embodiment where left andright end portions are cut first.

FIG. 5C illustrates a perspective view showing the UV irradiationprocess in the method for fabricating an LCD in accordance with a secondembodiment of the present invention.

In the UV irradiation, if UV is irradiated to the entire surface of theattached substrates, the UV ray may deteriorate device characteristicsof the thin film transistors on the substrates, and change a pre-tiltangle of the orientation film formed for the initial orientation of theliquid crystal.

Therefore, in FIG. 5C, the second embodiment of the present inventionsuggests irradiating the UV after a mask 950 c is placed between theattached substrates 200 and 300 and the UV irradiating device 900, formasking the regions where the dummy UV sealant 800 and the scribinglines are crossed, and the active regions inside the main UV sealant700.

As has been explained, the method for fabricating a liquid crystaldisplay panel of the present invention has the following advantages.

The UV irradiation with masking the crossed regions of the dummy UVsealant and the scribing lines makes cell cutting by the simultaneousscribing and breaking processes easier since the dummy UV sealant on thescribing lines is not hardened.

The UV irradiation with masking the active regions in the main UVsealant prevents the UV irradiation from deteriorating characteristicsof the thin film transistors, orientation films, and the like, formed onthe substrates.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the method for fabricatingan LCD panel of the present invention without departing from the spiritor scope of the inventions. Thus, it is intended that the presentinvention covers the modifications and variations of this inventionprovided they come within the scope of the appended claims and theirequivalents.

What is claimed is:
 1. A method for fabricating a liquid crystal displaypanel, comprising: forming a main UV sealant to surround a plurality ofunit cells and a dummy UV sealant on either one of first and secondsubstrates, the dummy UV sealant formed at an outside of the main UVsealant; dropping at least one droplet of liquid crystal onto either oneof the first and second substrates; attaching the first and secondsubstrates; irradiating a UV ray on the attached substrates with maskingregions where the dummy UV sealant and at least one scribing line arecrossed, thereby bonding the substrates; and cutting the bondedsubstrates into a plurality of unit cells.
 2. The method of claim 1,wherein the masking regions in the irradiating a UV ray on the attachedsubstrates includes masking upper and lower side portions of the crossedregions between the dummy UV sealant and the scribing line.
 3. Themethod of claim 1, wherein the masking regions in the irradiating a UVray on the attached substrates includes masking left and right sideportions of the crossed regions between the dummy UV sealant and thescribing lines.
 4. The method of claim 1, wherein the masking regions inthe irradiating a UV ray on the attached substrates includes masking anactive region inside the main UV sealant in addition to masking upperand lower side portions of the crossed regions between the dummy UVsealant and the scribing lines.
 5. The method of claim 1, wherein themasking regions in the irradiating a UV ray on the attached substratesincludes masking left and right side portions of the crossed regionsbetween the dummy UV sealant and the scribing lines.
 6. The method ofclaim 1, further masking an active region inside the main UV sealant. 7.The method of claim 1, wherein the main and dummy UV sealants includeone of monomer and oligomer each having both ends coupled to an acrylicgroup.
 8. The method of claim 1, wherein the main and dummy UV sealantsinclude one of monomer and oligomer each having one end coupled to anacrylic group and the other end coupled to an epoxy group.
 9. The methodof claim 1, further comprising heating the UV ray irradiated substrateswith masking crossed regions between the dummy UV sealant and thescribing lines, wherein the main and dummy UV sealants include one ofmonomer and oligomer each having one end coupled to an acrylic group andthe other end coupled to an epoxy group.
 10. The method of claim 1,wherein the scribing line is formed on the bonded substrates.
 11. Themethod of claim 1, wherein the cutting the bonded substrates into aplurality of unit cells is performed by scribing and breakingsimultaneously.
 12. The method of claim 1, further comprising forming atleast one column spacer on the first substrate.
 13. The method of claim1, wherein the main and dummy UV sealants are formed on the firstsubstrate, and the at least one droplet of liquid crystal is droppedonto the second substrate.